Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $166.47   10.545%   $184.0243   $184.02   $184.00   $184.00  
  Purchase #2 $54.82   6.388%   $58.3219   $58.32   $58.30   $58.30  
  Purchase #3 $200.82   4.660%   $210.1782   $210.18   $210.20   $210.20  
  Purchase #4 $166.97   10.174%   $183.9575   $183.96   $183.95   $184.00  
  Purchase #5 $233.47   13.131%   $264.1269   $264.13   $264.15   $264.10  
  Purchase #6 $201.28   6.815%   $214.9972   $215.00   $215.00   $215.00  
  Purchase #7 $236.70   6.615%   $252.3577   $252.36   $252.35   $252.40  
  7 purchase totals = $1,260.53       $1,367.9637   $1,367.97   $1,367.95   $1,368.00